The present invention relates to a writing instrument operated by a finger at a holding position.
Conventionally, there have been proposed various writing instruments each of which has a permanently exposed tip and a cap for protecting the exposed tip and preventing any contamination by the tip. Such writing instruments are commonly and mainly used as ball-point pens using an oil-based ink or a water-based ink and are kept mainly on a desk. In conventional ball point pens of this type, however, the cap should be taken off and put on when the pen is to be used and thus the handling thereof is troublesome.
With ball point pens using a water-based ink there have been reported accidents in which a cap which had been removed by mouth, became wedged in a child's throat causing suffocation.
There have been also for a long time proposed and used capless writing instruments or ball-point pens using an oil-based ink or a water-based ink. In such capless writing instruments a knocking type propelling mechanism is provided on the rear end of a body, or a rotating type propelling mechanism is used in which the propelling of the tip of the refill may be performed by mutually rotating the front portion and rear portion of the body. With these previously proposed capless writing instruments, when in use, it is necessary that the user change his or her grip on the body and then push the knocking mechanism or mutually rotate the front and rear portions of the body. Therefore, capless writing instruments of this kind have a disadvantage that handling is very troublesome. With capless writing instruments using water-based ink in which an ink reservoir and an air passage bore are so arranged and positioned that loss of the ink is minimized, there is provided a mechanism for retracting the tip and thus the refill, which may often be operated by a clip when being inserted into the user's pocket. This mechanism comprises a spring for forcing the refill to a retracted position. This spring has a strong spring tension and thus a core member in the refill may be displaced backwardly due to the shock which will occur at the retraction of the refill. This will also lead to cessation of writing.
Further, since the conventional capless writing instruments have no means for displaying retracting and propelling positions, the tip may be left unretracted. Moreover, when a writing instrument of the clip operating type is inserted into the user's pocket without operating the clip, the clothes of the user may be soiled by the exposed tip.
Furthermore, writing instruments of a double tip type are known which have an exposed and fixed tip on each side. One known pen of this type has different colored refills at the respective ends. Another has a pen having different type refills (for example, a water-based ink refill and a refill made of a suitable soft material into which an ink is infiltrated). Still another pen has ball-points or cores which have different diameters. With a ball-point pen of a water-based ink refill type it is necessary to provide caps for preventing any loss and leakage of the ink from the respective ball-points. With the ball-point pen of an oil-based ink refill type it is also necessary to provide caps for preventing contamination with ink from the respective tips.
Japanese Utility Model Publication No. 55-14552 and Japanese Patent Prepublication No. 53-127030 disclose a further knocking type writing instrument provided with writing tips at the both ends. In this conventional knocking type instrument, the user removes a pen-cap from one of the tips which is intended to be used for writing, fits it on a pen cap for the other tip, and pushes the fitted pen-caps so as to project the intended tip. In this case it is required that the user removes and replaces the pen-caps with both hands, which is troublesome.